Collies are herding dogs. The average collie can run up to 40 miles a day and be just fine. My dog runs off leash at a full run for 2 hours a day and still is not tired. When he did 3, he was barely tired.
As the other person mentioned, an off-leash dog park with a fence is a good idea. Walk around it with the dog to keep her moving and thinking.
Otherwise, you can get a remote collar. I have used one on my herding dog. Yes, I tried it on myself first. The very good ones are a little more expensive, but they are very gentle, the levels go up incrementally, and they are excellent back-up where your dog might endanger herself.
For example, one of the dog parks near me does not have a fence. It has coyotes in it, and the coyotes have led dogs into the nearby highways. In this case, the collar is good because it keeps the dog safe.
If you use a remote collar, make sure to have a professional help you with training or you could end up mentally harming your dog if you train incorrectly, inconsistently, or unkindly.
My dog is very "soft." He is not mentally damaged from his remote collar. He responds to just a vibration (like a cell phone) tone that some collars have. His is a Dogtra.